The present invention concerns a ship-propulsion system comprising a drive mechanism and a shaft directly connected to it and provided with a propeller.
Ships propelled by systems with only one drive mechanism can be subjected to considerable hazard when the mechanism malfunctions or fails. In the worst cases, the ship can become unmaneuverable and even totally lost. The maneuverability of ships that carry hazardous or very environmentally deleterious goods must in particular be guaranteed in emergencies.
The simplest solution is to install an accessory drive mechanism in the propeller shaft. Such accessory drive mechanisms include a motor that drives the shaft or propeller by way of a transmission, and the shaft must be uncoupled from the defective main drive mechanism by a separating mechanism. The thrust provided by such accessory or emergency drive mechanisms for application to the hull of the ship is much weaker than that of a main drive mechanism.
Such a approach can be inferred from the Lohmann & Stolterfoht prospectus, FLESALUS RDE 75153, published December 1993 and describing a "flexible" emergency ship-propulsion system. A pneumatically powered cogged clutch separates both the drive mechanism and the propeller, neither of which is illustrated. The coupling simultaneously acts as a bearing in transmitting the propeller's thrust. There is a drawback to this approach, however, in that there is play in the clutch and the resulting vibrations are difficult to deal with. Another drawback is that the clutch and bearing together require a special base to introduce the forces into the hull.
Known from Swiss Patent 173 968 is a combination ship-propulsion system wherein for example a piston device and a turbine can be engaged with a propeller shaft. To prevent damage to the drive mechanism if the shaft suddenly stops, a safety-ensurance clutch between the transmission and the propeller entirely disengages the shaft form the rest of the mechanism when a specified angular momentum is exceeded.